The present invention relates to a method and apparatus for purifying a continuous flow of noble gas; in particular, but not exclusively, the invention is concerned with the continuous production of ultra pure helium or neon (or mixtures thereof) where "ultra pure" means that contamination with any impurity gas or gases is less than one part in ten million by volume. Helium and neon gases of this purity have many uses including as sample carrier gas in modern analytical techniques, filling gases for discharge tubes and lasers, and purge gases in the semiconductor industry.